The invention is directed to improvements in turbocharged multi-cylinder internal combustion engines provided with fuel injection.
In engines of this kind, equipped with a turbocharger, the energy of the exhaust gas is utilized to drive the turbine, which in turn drives the compressor connected to it; as a result, the charge pressure of the combustion air supplied to the cylinders is increased, and the engine accordingly produces higher torque.
However, at low cylinder throughput such as is the case during overrunning of the engine used as a motor vehicle engine, or at low partial load, the air flow rate generated by the turbocharger is low. To increase the air flow rate in a known turbo-engine, an additional volume of exhaust gas is generated during overrunning and at partial load--that is, when the throttle valve is not fully opened--bypassing the cylinders in the exhaust gas conduit. This additional volume acts upon the turbine of the turbocharger and causes it to rotate faster than it does with only the quantities of exhaust gas that emerge from the cylinders. As a result, the turbocharger is kept to speed during overrunning and at partial load, and an adequate air flow rate is attained. The so-called "turbo lag" that normally arises in turbo-engines is avoided, and the overall response of the turbocharger is improved.
To generate the additional exhaust gas volume, combustion air that is under pressure in the intake conduit is supplied through the regulating valve, bypassing the cylinders, to the exhaust gas conduit when the throttle valve is closed or partly opened. The required fuel quantity is delivered through the cylinders, in which ignition is suppressed, to the exhaust gas conduit. The mixture of combustion air and unburned fuel ignites in the exhaust gas conduit, resulting in the additional exhaust gas volume that drives the turbine. Since only small quantities of fuel are needed here, the fuel injection into the cylinders does not have to occur upon every revolution of the crankshaft; instead, it can be performed only every m revolutions, m being an integer greater than or equal to 1.